The phases alone, being corrupted by residual OPDs, are of restricted
interest. It is however possible to combine them to form what is known
as closure-phase [1]}, that is the sum of three
phases measured by baselines forming a closed triangle. This
remarkable interferometric quantity (cf. the introduction to closure
phase by [2]}) exhibits a compelling property:
it rejects all residual pupil-plane phase errors. Moreover, because it
is determined from the analysis of the final science detector and not
on a separate arm wavefront sensor, it is also immune to non-common
path errors between the wavefront sensor and the science camera.
